Method and system for extracting cardiac parameters from plethysmographic signals

• US 7,604,603 B2
• Filed: 07/08/2004
• Issued: 10/20/2009
• Est. Priority Date: 03/26/2002
• Status: Active Grant

• Current Assignee: Adidas AG
• Original Assignee: VivoMetrics, Inc.
• Inventors: Keenan, Desmond, Sackner, Marvin, Inman, Dana Michael
• Primary Examiner(s): Marmor, II; Charles A
• Assistant Examiner(s): Natnithithadha; Navin
• Application Number:
  US10/886,994
• Publication Number:
  US 20060036183A1
• Time in Patent Office: 1,930 Days
• Field of Search: 600/481, 600/483, 600500-503, 600506-526, 600/536, 607 17- 26
• US Class Current: 600/500
• CPC Class Codes: A61B 5/0205 Simultaneously evaluating both cardiovascular conditions and different types of body conditions, e.g. heart and respiratory condition
• CPC Class Codes: A61B 5/02438 with portable devices, e.g. worn by the patient
• CPC Class Codes: A61B 5/0245 by using sensing means generating electric signals, i.e. ECG signals
• CPC Class Codes: A61B 5/0295 using plethysmography, i.e. measuring the variations in the volume of a body part as modified by the circulation of blood therethrough, e.g. impedance plethysmography
• CPC Class Codes: A61B 5/0535 Impedance plethysmography for measuring blood flow A61B5/0295
• CPC Class Codes: A61B 5/0816 Measuring devices for examining respiratory frequency measuring frequency of electric signals G01R23/00
• CPC Class Codes: A61B 5/1135 by monitoring thoracic expansion
• CPC Class Codes: A61B 5/6804 Garments; Clothes
• CPC Class Codes: A61B 5/721 using a separate sensor to detect motion or using motion information derived from signals other than the physiological signal to be measured
• CPC Class Codes: A61B 5/725 using specific filters therefor, e.g. Kalman or adaptive filters A61B5/316 take precedence
• CPC Class Codes: A61B 5/7278 Artificial waveform generation or derivation, e.g. synthesising signals from measured signals A61B5/327 takes precedence

Abstract

A method and system for extracting cardiac parameters from a plethysmographic signal is described wherein the plethysmographic signal is passed through a first filter to remove non-cardiac components of the signal. A second filter averages a plurality of cardiac cycles and cardiac parameters are extracted from the averaged cardiac signal.

Claims

1. A method for extracting a cardiac component from a plethysmographic signal comprising:

performing, by a computer, a frequency domain filtering operation on a plethysmographic signal producing a first filtered signal, the plethysmographic signal comprising a cardiac component responsive to cardiac motion and a non-cardiac component;

performing, by a computer, a time domain filtering operation on the first filtered signal to produce a second filtered signal, the second filtered signal comprising the cardiac component and a reduced non-cardiac component;

outputting the second filtered signal.

2. The method of claim 1 further comprising storing the output signal.

3. The method of claim 1 further comprising extracting from the output signal one or more cardiac parameters selected from the group consisting of stroke volume, cardiac output, pre-ejection period, peak ejection rate, and time to peak ejection rate.

4. The method of claim 1 wherein the frequency domain filtering operation comprises applying a band-pass filter having a lower comer frequency that varies in dependence on current heart rate.

5. The method of claim 1 wherein the time domain filtering operation comprises ensemble averaging timed by the occurrences of electrocardiographic R waves.

6. The method of claim 5 wherein the ensemble average of a signal at a current time sample is a weighted average of the signal at the current time sample with one or more signals at displaced time samples, the displaced time samples differing from the current time sample by one or more electrocardiographic R-wave intervals.

7. The method of claim 5 wherein R-wave intervals are determined by:

detecting R waves in a concurrent electrocardiogram; and

discarding a detected R wave that occurs in an ectopic temporal location or during a period of increased motion.

8. The method of claim 7 wherein an R-wave occurs in an ectopic temporal location if it occurs more that a threshold time before or after an R-wave occurrence time expected in dependence on a recent mean heart rate.

9. The method of claim 7 wherein an R wave occurs in a period of increased motion if it occurs when motion sensor signals exceed a threshold.

14. A computer readable medium comprising stored instructions for causing a processor to perform the method of claim 1.

10. A system for extracting a cardiac component from a plethysmographic signal comprising a processor coupled to a memory, wherein the memory includes stored instructions for causing the processor to

perform a frequency domain filtering operation on a plethysmographic signal producing a filtered signal , wherein the plethysmographic signal comprises a cardiac component responsive to cardiac motion and a non-cardiac component, and wherein the frequency domain filtering operation comprises applying a band-pass filter having a lower corner frequency that varies in dependence on current heart rate;

performing a time domain filtering operation on the first filtered signal to produce a second filtered signal, wherein the time domain filtering operation is based on the occurrences of electrocardiographic R waves, and wherein the second filtered signal comprises the cardiac component and a reduced non-cardiac component; and

output the second filtered signal.

11. The system of claim 10 wherein the processor further extracts from the output signal one or more cardiac parameters selected from the group consisting of stroke volume, cardiac output, pre-ejection period, peak ejection rate, and time to peak ejection rate.

12. The system of claim 10 wherein the processor performs ensemble averaging of a signal at a current time sample by forming a weighted average of the signal at the current time sample with one or more signals at displaced time samples, the displaced time samples differing from the current time sample by one or more electrocardiographic R-wave intervals.

13. The system of claim 12 wherein the processor further determines R-wave intervals by

detecting R waves in a concurrent electrocardiogram;

and

discarding a detected R wave that occurs in an ectopic temporal location or during a period of increased motion.

15. The system of claim 10 wherein the time domain filtering operation further comprises ensemble averaging.